50 MR. J. С. WILLIS ON А NEW NATURAL 
from the comparatively simple forms of the Chlamydatæ to the highly 
complex forms of the Achlamydatæ? How pass, for example, from the 
simple flower of Chlamydatæ with a monochlamydeous perianth and no 
spathe, to the achlamydeous flower with a spathe at the base of the stalk 
which occurs in the other group? How pass from a flower with one whorl 
of stamens and no staminodes to a flower with indefinite stamens, sometimes 
in more than one whorl, and as many staminodes? How pass from the 
small, simple, entire, moss-like leaf of the Chlamydatz to the large, much 
branched, and highly complicated leaf of the other group? How pass from 
an exstipulate leaf to a stipulate one with the very complex formation of 
branches in the “axil” of a second and lower stipule? How pass from the 
simple stem thalli of Chlamydatæ to the highly complex stem thalli that 
occur in the Achlamydatæ ? And so on, to other minor distinctions. 
On the mere ground of the impossibility of passing easily from one 
group to the other, therefore, it seems to be necessary to divide the existing 
family of Podostemaceæ (Hydrostachydaceæ being supposed already removed) 
into two. I propose to give to the group Chlamydatæ the name T'RISTICHACEÆ, 
from Тела, the genus first named in this group, and to reserve the name 
PoposteMACE for the remainder of the family, at present included in the 
sub-order Achlamydate. The former group will include the genera 
Tristicha, Lawia, and Weddellina, the latter the rest of the old family. 
Both families have practically the same geographical distribution. They 
occupy, in fact, the whole remaining part of the tropical and subtropical zone 
of the supposed ancient continent of Brazilia-Ethiopia, which had an arm 
running up through Madagascar to Ceylon and Peninsular India. The 
Tristichaceæ are practically confined to this region, while the Podostemaceæ 
go slightly beyond it into Java, Assam, and the United States. We shall 
return in a later paper to the subject of distribution of this group. 
The two families thus constituted agree in many characters, but not 
sufficiently, it seems to me, to justify their being united. Both are herbs of 
rapidly moving water, attached to rocks by ereeping roots (exceptions), on 
which are borne secondary shoots of the most various size and form. Their 
flowers appear above the water (exceptions). They have thick and fleshy 
placentas, on which are borne numerous, anatropous, horizontal ovules 
(exceptions). The fruit is a septifragal capsule (exceptions), and there is no 
style (exceptions). The seeds are exalbuminous, and the embryology is 
peculiar, and much the same in both families. 
Placing the families, then, for the present in Rosales, near to the Saxi- 
fragaceæ (though I am by no means sure that this is the proper place), they 
occupy a separate sub-group, Podostemonines, for which Engler gives the 
following characters : submerged annual plants, flowering at the fall of the 
water, only resembling the Saxifragaceæ in the placenta ; completely trans- 
formed by adaptation to peculiar conditions of life. 
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